Spinning method

ABSTRACT

Liquid polymeric materials, in a fiber spinning operation, are extruded through extrusion passageways of a spinneret plate. The passageways are designed to establish an essentially constant extensional strain rate condition for flow of liquid.

United States Patent 1111 LaNieve Dec. 9, 1975 SPINNING METHOD 3,006,02610/1961 Martin 6t 21]. 425/464 3,210.45l [Cl/I965 Manning et al 425/464[75] memo" Henna Lameve1 summti 3.382535 5/[968 Ferrari 264/177 FAssignee: celanese C rp rati N w Y k, Santeangelo r r i r i i I I Y v vv v FOREIGN PATENTS OR APPLICATIONS [22] Filed: Aug. 10, 1973 246,82811/1960 Australia .5 425/464 [2 AWL 3 7 7 OTHER PUBLICATIONS PolymerProcessing by J. M. McKelvey, pp. 8797, [52 us. (:1 ,1 264/40; 264/176F; 264/177 F; John wley Sons New York 1962' 264 204' 264 7 511 1111. 0.F02M 1 1 /30 pr'mary Emmmekjay W00 [58] Field of Search 425/464; 264/177F, 176 F,

264/40, 204, 207 ABSTRACT L1qu1d polymeric materials, in a fiberspinning opera [56] References Ci tion, are extruded through extrusionpassageways of :1 UNITED STATES PATENTS spinneret plate. The passagewaysare designed to es 2 21 l 946 8/940 G 425/464 tablish an essentiallyconstant extensional strain rate raves 4. 1 2,341,555 2/1944 16m I I I II I 425/464 Condmon for flow of hquld 2,742 667 4/1956 Clauzeau et al425/464 13 Claims, 5 Drawing Figures U.S. Patent Dec. 9, 1975 FIG.1

FIG.2

M. w ilililii i- SPINNING METHOD BACKGROUND AND OBJECTS OF THE INVENTIONThis invention relates to the spinning of synthetic filaments. Moreparticularly, this invention relates to a novel method and apparatus forthe spinning of synthetic filaments utilizing a spinneret nozzledesigned to establish an essentially constant extensional strain rate.

In connection with the production of filaments from man-made fiberforming materials, it has been common to utilize spinnerets including aplurality of exit passageways in the form of nozzles or orificesmachined in a spinneret plate. A liquid comprising a polymer melt or asolution of a polymer in an appropriate solvent is extruded throughthese nozzles in the filament forming process.

As will be appreciated, the profile of such spinneret nozzles has beenthe subject of considerable research efforts. In this connection,reference may be had to U.S. Pat. No. 3,537,135 (issued Nov. 3, I970),U.S. Pat. No. 3,303,530 (issued Feb. 14, I967), U.S. Pat. No. 3,210,451(issued Oct. 5, 1965), U.S. Pat. No. 3,227,009 (issued Jan. 4, l966),and U.S. Pat. No. 3,174,183 (issued Mar. 3, 1965) for disclosures ofspinnerets with exit passageways having a variety of profiles.

An important consideration in fluid flow through a spinneret passagewayof any given profile is that of fluid pressure drop. The pressure dropacross a spinneret can be expressed as the sum of the viscousdissipation in the passageway and the entrance and exit flows, thepressure due to kinetic energy effects, and that due to storage ofelastic energy.

Another important consideration in spinneret fluid flow is that ofextrudate swell or die swell, i.e. the ratio of the fibercross-sectional area after it passes the exit orifice of the spinneretexit passageway to the crosssectional area of that exit orifice. Dieswell has a direct effect on draw ratios and fiber elongation.

For example, in the case of spinning polyethylene terephthalate (PET),increased extrudate swell resulting from increased spinning productivitywould produce decreases in after-draw ratio. Similarly, in con nectionwith production of dry spun fibers from cellulose triacetate (CTA),increased extradate swell would reduce fiber elongation.

It has been found that extrudate swell in connection with flow through acapillary is inversely related to the ratio of the capillary length toits diameter. However, under high spinning productivities, attempts toreduce extrudate swell by increasing that ratio may produce an excessivepresure drop due to viscous dissipation.

Since costs associated with the operation of spinning equipment areconsiderable, adequately high spinning productivity must be maintained.

It would, therefore, be highly desirable to provide a novel spinningmethod and apparatus based upon a passageway profile designed toadvantageously accomodate desirable spinning productivity consistentwith acceptable pressure drop and extrudate swell. Accordingly, it is ageneral object of the present invention to provide such a novel spinningmethod and apparatus.

In spinning operations, one important viscosity consideration is that offluid pressure drop in spinneret flow due to viscous dissipation. Underhigh productivity spinning conditions, viscous pressure drop oftenbecomes excessive. As such, viscous pressure drop to some extentconstitutes a limiting factor on spinning productivity. Since the costsassociated with the operation of spinning equipment are considerable, itwould be highly desirable to provide for increased spinning productivityby minimizing viscous pressure drop or to provide for a viscous pressuredrop consistent with a given spinning productivity.

In realizing this object, the present invention departs from those priorart approaches to design of spinneret nozzle profiles which have beengoverned primarily by direct viscosity considerations, and perhaps, tosome extent, inertial and turbulence considerations.

In this connection, the present invention embodies a recognition thatspinneret flow for fluids generally classified as viscous, such as PETmelts or CTA solutions, is dominated by elastic" forces. Moreparticularly, according to the present invention a nozzle profile isprovided so as to establish an essentially constant extensional strainrate, viz. a constant change in veloc ity with respect to theincremental distance of fluid travel (an elastic force consideration).In this fashion the flow condition for the liquid is such as to providefor a low total pressure drop. At the same time adequate spinning speedsmay be employed with acceptable die swell.

The essentially constant extensional strain rate leads to a low totalpressure drop through several mechanisms. First, since the elasticpressure drop contribution to the total pressure drop is governed by themaxi mum extensional strain rate, a low constant extensional strain ratemay be chosen to reduce that contribution as compared with prior artnozzle profiles. Secondly, as hereinafter more fully described, at achosen constant extensional strain rate, the viscous pressure drop isminimized. In addition, the gentle streamline entry flow provided by thenozzle profile of the present invention is believed to reducedissipation due to vena contracta type eddies.

It may be here noted that an apparently similar profile has beenproposed for an entirely different purpose, namely, the design of aminimum length die to be used for extruding on a wire, plastics whichare subject to melt fracture. (See U.S. Ferrari Pat. No. 3,832,535,issued May I4, 1968.) Considerations directed toward elimination of meltfracture and minimizing die length in the environment of extrudingplastics on a wire are unrelated to the present invention, in thatpolymers involved in the contemplated spinning operations do not exhibitany significant melt fracture in the range of op erating conditionsselected in contemplation for practice of the present invention.

Consistent with the foregoing, it is, therefore, a further object of thepresent invention to provide a novel spinning method and apparatuswherein an essentially constant extensional strain rate is establishedfor flow through a spinneret nozzle.

It is a further object to the present invention to provide such a novelspinning method and apparatus wherein adequate spinning speeds may beemployed with acceptable die swell.

It is yet another object of the present invention to provide such anovel spinning method and apparatus wherein a low total pressure drop isproduced.

It is still another object of the present invention to provide such anovel spinning method and apparatus which minimizes breaking offilaments in a spin line,

and thus minimizes the occurence of incomplete packages. In thisconnection, it is believed that breaking of filaments in a spin linemight, in some respects, be attributable to faults or impurities, in thespinning material. The particular improved spinneret flow producedaccording to the present invention is thought to minimize the adverseconsequences attributable to such faults or impurities.

SUMMARY OF PREFERRED EMBODIMENTS OF THE INVENTION A preferred form ofthe invention intended to accomplish at least some of the foregoingobjects entails the spinning of fibers through the provision of aspinneret plate for extruding polymeric materials and including at leastone converging extrusion passageway having an entry opening and an exitorifice, with the passage profile being designed to establish anessentially constant extensional strain rate.

Spinning speeds in the range of about 500 to I500 meters per minute inthe case of solution spinning and 500 to 6000 meters per minute in thecase of melt spinning are usually appropriate, with about 1000 metersper minute and about 1200 to 3000 meters per minute being preferredrespectively for dry and wet solution and for melt spinning. Solutionspinning temperatures of about 50 to l lC, preferably about 90C areusually contemplated. For melt spinning, temperatures in the range ofabout 275 to 330C, preferably 285 to 300C, are involved.

Preferably the approach angle, defined as the angle of intersectionbetween the axis of the converging extrusion passageway and the tangentto the wall of that passageway at the entrance opening, is between aboutto 45.

The passageway (i.e. the spinneret plate thickness) and exit orificearea may vary, with lengths in the range of about 0.020 to 0.060 inchesfor solution spinning and 0.1 to 0.6 inches for melt spinning, and areasin the range of about 3 X 10 to 50 X 10 square centimeters (solutionspinning) and about l X l0 to 50 X 10 square centimeters (melt spinning)being desirable.

In accordance with the present invention, it will be appreciated thatspinning of fiber-formin g materials by solution spinning (wet or dry)or melt spinning (without significant melt fracture in the range ofoperating conditions selected for the materials in contemplation forpractice of the present invention) of any suitable polymeric materials,such as polyamides, polyesters, acrylics, polyimides, cellulosics, vinylchloride and vinylidene cyanide polymerics and the like, may bepracticed. Particular applicability of the present invention may befound in high speed spinning of cellulose esters or polyesters,especially polyethelene terephthalate.

For example, the process is of particular value in the dry solutionspinning of cellulose triacetate from solution in a solvent comprising amajor amount of a halo genated hydrocarbon such as methylene chloride.

In this connection, as employed herein, cellulose triacetate hasreference to cellulose acetate having fewer than about 0.29 andpreferably fewer than about 0.12 free hydroxyl group per anhydroglucoseunit of the cellulose molecule, i.e., an ac etyl value calculated ascombined acetic acid by weight of at least about 59 percent andpreferably at least about 61 percent.

Advantageously, its intrinsic viscosity ranges from about 1.5 to 2.5 andis preferably about 2, and it is pres ent in the dope to a concentrationranging from about 20 to 25 percent. In place of methylene chloride, thedope solvent may comprise other halogenated lower alkanes such asethylene dichloride or propylene chloride. Preferably, up to about 15percent by weight of the dope solvent comprises a lower alkanol such asmethanol, ethanol, isopropanol, etc. The preferred dope solvent ismethylene chloride-methanol in the proportions of about -10 by weight.

The cross-sectional configuration of the nozzle employed in accordancewith the present invention is preferably symmetrical about the nozzleaxis, with a circular cross-section being the preferred form. However,non-circular configurations conventional in the spinning art, such asfor example those depicted in US. Pat. No. 3,303,530, issued Feb. 14,1967, are also contemplated.

Other objects and advantages of the present invention will becomeapparent from the following detailed description thereof with referenceto the accompanying drawings in which like numerals indicate likeelements, and in which:

THE DRAWINGS FIG. is a plan view of a spinneret in accordance with thepresent invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is an enlarged sectional view showing the profile of the exitpassageway of the spinneret of FIGS. 1 and 2;

FIG. 4 is an enlarged sectional view showing the passageway of FIG. 3contiguous, adjacent its entry end, with a frusto-conical passageway;

FIG. 5 is a schematic illustration of a dry spinning op eration inaccordance with the present invention.

DETAILED DESCRIPTION With reference now to FIG. 1, a spinneret or jet 10in accordance with the present invention may be seen. This spinneret ismade of any suitable material such as stainless steel.

As may be seen FIG. 2, the spinneret is generally cupshaped. The cupbottom indicated at 12 is provided with a plurality of circumferentiallydisposed, spaced apertures or exit passageways l4 therethrough.

During spinning operations, a liquid comprising a polymer melt or asolution of a polymer in an appropriate solvent is supplied to thespinneret 10 and is extruded through the exit passageways I4 in thefilament forming process. An enlarged view of a preferred forms of theexit passageway 14 may be seen in FIGS. 3 and 4.

Each passageway 14 is in the form of a converging nozzle, the profile ofwhich is hereinafter more fully described, that terminates in an exitorifice 16. After flow into the entry orifice 17, through the nozzlepassageway and out the exit orifice l6, elastic energy stored in theliquid is recovered so as to result in extrudate swell or die swell.This storage of elastic energy occurs by reason of the extensional flowof the fluid.

In FIG. 5 there is shown a dry spinning cabinet 20 to which dope issupplied through a pipe 22. The liquid dope is extruded through thespinneret 10 of FIGS. l-3 with no intervening plating of the spinneret.I-Iot air may be admitted to the cabinet 20 through a suitable conduit23 and may be exhausted through a suitable conduit 24 along with vaporsof the dope solvent. The filaments 26 leaving the spinneret 10 throughthe extrusion passageways 14 are directed about a guide 28 and out ofthe cabinet at a location indicated at 30. The filaments are pulled as ayarn 32 by suitable draw rolls 34. The yarn 32 by suitable draw rolls34. The yarn 32 passes through a guide 36 and is twisted and taken up ona bobbin 38 by a conventional collector such as a ring spinner 40.

With renewed reference to FIG. 3, the nozzle profile in accordance withthe present invention may be more fully appreciated. In FIG. 3, theradius of the exit ori- 1 fice 16 is indicated by R. The nozzlepreferably is circular in transverse cross-section, and has smooth,gradually curving walls 18 in the form of a surface of revolutiondefined by a generatrix moving about the central axis 19 of thepassageway 14. The wall profile, conforming to the shape of thisgeneratrix, provides an essentially constant extensional strain rateduring flow of the polymeric material through the passageway 14 by beingdesigned to essentially respond to the following cubic equation:

f= z+ll 2 where:

R is the radius of the exit orifice l6;

r u is the wall radius measured perpendicular to the axis 22;

Z is the distance along the axis 19 of the nozzle measured from the exitorifice 16; and

A is a constant hereinafter more fully described.

One the criterian of constant extensional strain rate is selected, theforegoing Equation (1) may be derived by integrating the followingequation:

61 152 x where:

6v/6Z is the extensional strain rate represented by the partialderivative of velocity (V) with respect to distance measured from theexit orifice 16 along the nozzle axis 19; and

K is a constant, while recalling that:

V is the fluid velocity;

no is the wall radius as defined for equation (1); and

Q is the volumetric flow rate. and while also recalling the limitcondition that )1!) is equal to R [as defined for equation (l)]at theexit orifree 16.

Preferably the constant A of Equation (l) is determined by equating theconstant extensional strain rate K of Equation (2) with the maximumextensional strain rate for a conical spinneret wherein the die swell isacceptable (hereinafter referred to as equivalent conical spinneret").Then,

K Ev/EZ maxi cone where:

Sv/SZ max. cone is the maximum extensional strain 55 rate for theequivalent conical spinneret. The well known equation for the wallprofile of a conical spinneret is:

rm Z tan 0 4K A P v Q where:

rm and Z are as defined in Equation l); and 6 is the half angle of theequivalent conical spinneret,

preferably in the range of 2 to 7%" 6 By combining equations (3) and(5), and recognizing that for a cone 5r/8Z is a maximum at the exitorifice 16 where Z is zero and rm is R, it will be determined that:

tan

52 maxvcone= 2 (6] where:

7,; is 4Q/1rR the wall shear rate.

Equations (2) through (6) may then be combined and integrated to produceequation (1) where A of equation (l) will be defined as:

V 2 tan where:

no is the wall sheer stress; and K, and n are fluid constants,Describing the viscous pressure drop A P v as:

arm

where:

Z indicates the axial position where no becomes infinite and combiningEquations (8) and (9) yields:

APv=2K,( (10) When equation (3) is partially differentiated with respectto Z to produce:

and Equation (ll) is rearranged and substituted in Equation (10), itwill be seen that Since 5v/8Z appears in the denominator of Equation(l2), the largest possible value of 8v/5Z provides the smallest viscouspressure drop (APv) However, the provision for a constant extensionalstrain rate inherently imposes the constraint that:

fir/BZ 6 6v/8Z maximum. (l3) leading to the conclusion that the viscouspressure drop of Equation (I2) is minimized by the extensional strainrate being at a constant that is also the maximum.

With reference now to FIG. 4, a further nozzle passageway that may beemployed according to the present invention may be seen. The passagewayof FIG. 4 is comprised of the nozzle passage 14 of FIG. 3 contiguouswith a passageway extension 42 in the form of a frusto-conicalcountersink. It has been found that manufacturing of the spinneret witha passageway 14 profile establishing an essentially constant extensionalstrain rate as discussed above is more convenient when such acountersink is provided.

To aid in insuring a smooth flow transition, it is, however, desirablethat the intersection of the conical section 42 with the passageway 14be such that the walls of the cone are tangent to the walls 18 of thepassageway 14 at its entry orifice 17. If such tangency is not provided,and the cone makes a steeper angle than the tangent then the extensionalstrain rate in the conical section 42 will be greater. As such, thechosen die-swell characteristics will not be met, and viscous pressuredrop will be greater than the minimum which the constant extensionalstrain rate otherwise would provide.

Although the invention has been described with reference to preferredforms thereof, it will be appreciated that additions, substitutions,modifications and deletions may be made without departing from thespirit and scope of the invention as defined in the appended claims:

What is claimed is:

I. In a method of spinning fibers from fiber-forming, liquid polymericmaterial utilizing a spinneret for extruding said material through atleast one converging nozzle passageway having an entry opening and anexit orifice. the improvement comprising establishing an essentiallyconstant extensional strain rate condition for flow of said liquidthrough said passageway by providing a nozzle passageway bounded bygradually curving walls having a profile described essentially by theequation R is the perpendicular distance between an axis of thepassageway and the nozzle wall at the exit orifree;

r w is the perpendicular distance between nozzle wall and points alongthat axis;

Z is the distance along that axis measured from said exit orifice; and

A is a constant.

2. The method according to claim 1 wherein said protile is defined by asurface of revolution defined by a generatrix described by said equationand moving about said axis in a generally circular path.

3. The method according to claim 2 wherein the constant A in saidequation is defined by -2 tan B/R where 0 is the conical half angle ofan equivalent frustoconical passageway for establishing a maximumextensional strain rate essentially equal to said essentially constantextensional strain rate.

4. A solution spinning method according to claim 3 wherein said liquidmaterial consists essentially of cellulose acetate and wherein saidmaterial is extruded at spinning speeds in the range of about 500 to1500 meters per minute at spinning temperatures of about 50 to ll0C.

5. A melt spinning method according to claim 3 wherein said liquidmaterial consists essentially of polyethylene terephthalate and whereinsaid material is extruded at spinning speeds in the range 500 to 6000meters per minute at spinning temperatures of about 275 to 330C.

6. The method according to claim 1 wherein said passageway is contiguouswith and tangent to the walls of a frusto-conical passageway.

7. The method according to claim 1 wherein said liquid materialcomprises polyethylene terephthalate.

8. The method according to claim 1 wherein said liquid materialcomprises cellulose acetate.

9. The method according to claim 1 wherein said liquid materialcomprises cellulose triacetate.

10. A solution spinning method according to claim I wherein saidmaterial is extruded at spinning speeds in the range of about 500 to1500 meters per minute.

11. A melt spinning method according to claim 1 wherein said material isextruded at spinning speeds in the range of about 500 to 3000 meters perminute.

12. A solution spinning method according to claim 1 wherein the spinningtemperature is in the range of about 50 to ll0C.

13. A melt spinning method according to claim 1 wherein the spinningtemperature is in the range of about 275 to 330C.

UNITED STATES PATFNT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,925,525 Page I of 5 DATED December 9 1975 |NVENTOR(S)Herman L. LaNieve It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 5, line 21, equation (1) should read:

line 24, "rm" should read r line 29 "One" should read Once line 32,equation (2) should read:

3V az K;

line 34, "(W/ 52" should read BV/BZ line 39, equation (3) should read:

lines 42, 44 and 65, "rm" should read r line 52,

equation (4) should read:

U NITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 1 3,925,525 Page 2 f 5 DATED December 9, 1975 INVENTOR(S)Herman L. LaNieve It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

line 55, "(iv/62" should read BV/GZ and, line 59, equation (5) shouldread:

I Z tan 8 Column 6, line 2, "Sr/62" should read ar/az lines 3 and 44,"rw" should read r -lines 4-9, equation (6) should read:

i; tan 6 az 2 R max cone lines 14-18, equation (7) should read:

A 2 tan 6 lines 30-34, equation (8) should read:

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION Page3 of 5 PATENT N0. 3,925, 525

DATED December 9 |NVENTOR(S) Herman L. LaNieve It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

line 35, "Tm" should read 1 lines 37 and 68 "A should read AP read shearline 35, "sheer" should lines 38-42, equation (9) should read:

r; NTTED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,925,525 Page 4 of 5 DATED December 9 1975 INVENTOR(S)Herman L. LaNieve It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

lines 60-65, equation (12) should read:

rm an AP) -4K Q n+1 2 dr n r and aZ w r =R lines 66 and 67, "6V/6Z"should read 8V/8Z 82 Z maximum Claim 1, line 11, the equation shouldread:

1 and UNITED sTATEs PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION PATENT NO. 3,925,525 Page 5 of 5 DATED December 9, 1975mvgmoms) Herman L. LaNieve It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

line 16, "rm" should read r Signed and Scaled this Twenty-second Day ofMay 1979 [SEAL] DONALD W. BANNER RUTH C. MASON Arresting OflicerCommissioner of Patents and Trademarks

1. IN A METHOD OF SPINING FIBERS FROM FIBER-FORMING, LIQUID POLYMERICMATERIAL UTILIZING A SPINNERET FOR EXTRUDING SAID MATERIAL THROUGH ATLEAST ONE CONVERGING NOZZLE PASSAGEWAY HAVING AN ENTRY OPENING AND ANEXIST ORIFICE, THE IMPROVEMENT COMPRISING ESTABLISHING AN ESSENTIALLYCONSTANT EXTENSIONAL STRAIN RATE CONDITION FOR FLOW OF SAID LIQUIDTHROUGH SAID PASSAGEWAY BY PROVIDING A NOZLE PASSAGEWAY BOUNDED BYGRADUALLY CURVING WALLS HAVING A PROFILE DESCRIBED ESSENTIALLY BY THEEQUATION
 2. The method according to claim 1 wherein said profile isdefined by a surface of revolution defined by a generatrix described bysaid equation and moving about said axis in a generally circular path.3. The method according to claim 2 wherein the constant A in saidequation is defined by -2 tan theta /R3 where theta is the conical halfangle of an equivalent frustoconical passageway for establishing amaximum extensional strain rate essentially equal to said essentiallyconstant extensional strain rate.
 4. A solution spinning methodaccording to claim 3 wherein said liquid material consists essentiallyof cellulose acetate and wherein said material is extruded at spinningspeeds in the range of about 500 to 1500 meters per minute at spinningtemperatures of about 50* to 110*C.
 5. A melt spinning method accordingto claim 3 wherein said liquid material consists essentially ofpolyethylene terephthalate and wherein said material is extruded atspinning speeds in the range 500 to 6000 meters per minute at spinningtemperatures of about 275* to 330*C.
 6. The method according to claim 1wherein said passageway is contiguous with and tangent to the walls of afrusto-conical passageway.
 7. The method according to claim 1 whereinsaid liquid material comprises polyethylene terephthalate.
 8. The methodaccording to claim 1 wherein said liquid material comprises celluloseacetate.
 9. The method according to claim 1 wherein said liquid materialcomprises cellulose triacetate.
 10. A solution spinning method accordingto claim 1 wherein said material is extruded at spinning speeds in therange of about 500 to 1500 meters per minute.
 11. A melt spinning methodaccording to claim 1 wherein said material is extruded at spinningspeeds in the range of about 500 to 3000 meters per minute.
 12. Asolution spinning method according to claim 1 wherein the spinningtemperature is in the range of about 50* to 110*C.
 13. A melt spinningmethod according to claim 1 wherein the spinning temperature is in therange of about 275* to 330*C.